The present invention relates generally to network interfacing, and more particularly, to a system for gain adjustment within a base band signaling network interface.
Networks serve the purpose of connecting many remotely spaced computing devices, such as desk top computers, file servers, printers etc, to each other so that valuable computing resources can be shared.
Communication protocols and standards for networks have been developed to standardize the way in which data frames are transmitted across the physical media of the network.
Ethernet is a popular network architecture based on carrier sense multiple access/collision detection (CSMA/CD) access control. The original Ethernet specification operated on a multi-drop bus topology in which all devices were coupled to a multi-drop bus in parallel. However, today the term Ethernet is often used to additionally refer to the IEEE 802.3 10BASE-T and 100BASE-T specifications which utilize a multi-drop logical bus topology although a star bus physical topology is used to improve reliability and facilitate troubleshooting.
In each of the 10BASE-T and 100BASE-T specifications, the number 10 or 100 refers to the transmission speed, the term xe2x80x9cBASExe2x80x9d indicates that frames of data are being transmitted at base band, and the letter xe2x80x9cTxe2x80x9d specifies a twisted pair physical medium.
A star bus physical topology provides for each computing device to be coupled to a central hub via a dedicated communication link between the hub and the computing device. Each communication link comprises a transmit link and a receive link to provide for full duplex communications.
Because the system utilizes a logical multi-drop bus topology, the hub repeats frames to all nodes, and each device contends for access to the transmission medium as if all were connected along a single bus.
Because the transmissions are at base band, in theory, a receiver could simply sample the incoming signal with an A/D converter being clocked at the known base band data rate and in phase with the transmitter to recover the transmitted data.
However, the network topology tends to distort the data signal due to branch length, reflections, and electrical interference. As such, a variable gain amplifier is typically used. The amplifier conditions the signal, in accordance with a gain setting of the amplifier, prior to the A/D converter to assure that the signal parameters are within the dynamic range of the A/D converter.
Typically, the gain of the amplifier is set using a closed loop feedback system. A problem exists in that the circuitry comprising an analog closed loop feed back system can be large and costly. Furthermore, the circuits can be cumbersome to optimize for high data rate systems.
Therefore, based on recognized industry goals for faster data rate transmissions, reduced error rates, and reduced size and cost, what is needed is a device and method for adjusting input gain for an amplifier in a base band network receiver that does not suffer the disadvantages of known systems.
A first aspect of the present invention is to provide a network receiver configured for receiving a base band data signal from a network transmitter via a network medium. The network receiver comprises a variable gain input amplifier for amplifying a received signal according to one of a plurality of amplifier gain settings. The amplifier outputs an amplified base band signal. An A/D converter generates a sequence of digital sample values representing the amplified baseband signal. A range detection circuit determines a range of digital sample values during each of a plurality of monitoring intervals during a training time period and an automatic gain control circuit calculates one of the plurality of amplifier gain settings in response to at least one range value determined during the training time period and couples the amplifier gain settings to the variable gain input amplifier.
The network receiver may further include a physical layer control unit determining the training time period and the training time period may correspond to a time period during which the network transmitter is transmitting a pseudo noise signal.
The network receiver may further include a logarithmic look up table generating a log value representing the range and an adder calculating a difference between the log value and a reference level. A loop gain multiplier may multiplying the difference between the log value and the reference level by one of a plurality of loop gain constant values to generate a loop gain product.
The plurality of loop gain constants may include a high value useful for achieving rapid convergence during a first portion of the training time period, a low value useful for achieving convergence during a second portion of the training time period, and zero useful for locking the gain during a third portion of the training time period. An integrator may integrate a sequence of the loop gain products to generate the gain setting.
The range detection circuit may include a maximum sample value register storing the maximum digital sample value during the monitoring interval and a minimum sample value register storing the minimum digital sample value during the monitoring time interval. An adder may calculate the difference between the maximum sample value and the minimum sample value to generate the range.
A second aspect of the present invention is to provide method of determining a gain setting for a variable gain input amplifier in a receiver configured for receiving a base band signal from a network medium. The method comprises: a) digitizing an amplified received signal from the variable gain input amplifier to generate a sequence of digital sample values; b) determining a range of digital sample values during each of a plurality of monitoring intervals during a training time period; d) calculating an amplifier gain setting at least one range value determined during the training time period; and e)coupling the amplifier gain settings to the variable gain input amplifier. The training time period may correspond to a time period during which the network transmitter is transmitting a PN signal.
The method may further determining a logarithmic value representing the range and comparing the logarithmic value representing the range to a reference level value to generate a difference value. The difference value may be multiplied by one of a plurality of loop gain constant values to generate a loop gain product.
The plurality of loop gain constants may include a high value useful for achieving rapid convergence during a first portion of the training time period, a low value useful for achieving convergence during a second portion of the training time period, and zero useful for locking the gain during a third portion of the training time period. An integrator may integrate a sequence of the loop gain products to generate the gain setting.
The method may further include integrating a sequence of loop gain products to generate the gain setting and the step of determining the range of digital sample values may include determining the maximum digital sample value during the monitoring interval and determining the minimum sample value during the monitoring interval and calculating the range as the difference between the maximum sample value and the minimum sample value.